Roof bolts are conventionally installed vertically in mine roof openings to support the mine roof. When, for safety's sake, a bolt must be used which is longer than the height of the mine passage, the bolt must first be bent in order to insert the upper end thereof into the mine roof opening. After partial insertion in the opening, the bent bolt must then be straightened to permit full insertion of the bolt into the opening, following which the bolt is rotated to anchor it by mechanical anchors or resin.
In the past, the bending and straightening of roof bolts have been carried out manually in a laborious and slow procedure which has resulted in many injuries to workers including back strains and falls caused by the worker's feet slipping off the rods while bending them.
More recently, the bolts have been notched at the point they are to be bent, which increases the cost of manufacture thereof. Although notching reduces the force necessary to bend the bolt, the notches also weaken the bolts by as much as 40%, thereby considerably increasing the danger that roof fall will occur due to breakage of the bolt at the location of the notch.